The contact between an electrode and the n-type GaN layer of a group III nitride semiconductor allows obtaining relatively good low contact resistance value by the constitution of the metals such as Ti/Al/Au or so. For example, the method of forming n-type contact electrode laminating the metal having a higher melting point than Al by sequentially forming Ti and Al on the GaN layer of the n-type semiconductor layer as the n-type contact electrode (for example, refer to Patent document 1). Patent document 1 recites Au, Ti, Ni, Pt, W, Mo, Ta and Cu or so as the metal having higher melting point than Al, and it describes that Au which has good bonding with the Ti and Al is particularly good.
In said Patent document 1, the electrode laminating Ti layer, Al layer, Au layer on the n-type GaN layer in said order is shown as the specific example of the n-type contact electrode. The constitution of said n-type contact electrode is shown in FIG. 1. Such n-type contact electrode is formed by the following steps. Specifically, in the Patent document 1, as for the method for forming the n-type contact electrode, the steps of carrying out the dry etching to the n-type GaN layer (the contact layer), then sequentially forming the electrode metal made of Ti, Al, Au on said contact layer, and finally carrying out the heat treatment at 400° C. or higher, specifically 600° C., is described. By forming the contact electrode on the n-type GaN layer by above mentioned method, it is shown that a good contact resistance value can be obtained and the contact electrode having high bonding strength with the n-type GaN layer can be obtained.